In general devices which are used to both ventilate an enclosure and prevent rain from entering, are baffled or louvered devices. These baffles provide a tortuous path for the air or gas to travel, causing the heavier-than-air rain drops to precipitate. The greater the tortuosity, the more efficient the device becomes in preventing rain from entering. However, increasing the tortuosity of the path increases the resistance to air flow, reducing the efficiency of the baffle or louvre as a ventilator. The tortuous path also reduces the light which may pass through the baffle, as well as making incoherent the light rays from an image.